This invention pertains to lamp systems for over-the-road vehicles and in particular to a novel relay adapter circuit for adapting the existing stop/turn signal systems of a motor vehicle with the existing lamp system on a trailer towed by the motor vehicle.
Where a trailer is towed by a motor vehicle, the existing stop and turn signal lamp systems on the vehicle must be electrically connected with lamps on the trailer so that the trailer lamps can also provide the appropriate stop and turn signal indications to any vehicle which may be following the trailer. The trailer typically has a single lamp circuit on each side and may have one or more lamps in each circuit. Where the existing motor vehicle stop lamp and turn signal lamp systems incorporate stop and turn signal functions in a single lamp circuit on each side of the vehicle, the existing lamp circuit on each side of the trailer may be connected in parallel with the load in the corresponding vehicle lamp circuit and a heavy duty turn signal flasher may replace the existing vehicle flasher for handling the extra electrical load occasioned by the trailer lamps. Because the existing vehicle stop lamp and turn signal lamp systems of this type utilize a common lamp (or lamps) on each side of the vehicle for combined stop and turn signal function capability, the connection of the trailer lamps in parallel with the vehicle lamps causes the trailer lamp on each side to operate in exactly the same manner as the vehicle lamp (or lamps) on the corresponding side. Where the motor vehicle has separate stop and turn signal lamp circuits on each side of the vehicle and where the trailer likewise has separate stop and turn signal lamp circuits on each side, each trailer circuit may be connected directly in parallel with the load in the corresponding vehicle lamp circuit and a heavy duty flasher may replace the existing vehicle flasher to handle the additional load. However, where the motor vehicle has separate stop and turn signal lamp circuits on each side, a problem arises where the trailer has only a single lamp circuit on each side.
The present invention provides a solution to this problem so that the single lamp circuit on each side of the trailer can accomplish both stop and turn signal functions. Briefly, the present invention provides, in a presently preferred embodiment thereof, a relay adapter circuit which is electrically connected with the existing vehicle stop lamp and turn signal lamp systems and with the lamp systems on the trailer. The adapter can be readily electrically connected with both the vehicle and the trailer without need to rewire any circuits, to add extra lamps on the trailer, or even to replace existing vehicle components, such as the flasher, with heavier duty devices. Moreover, the adapter itself comprises only a small number of components and hence is quite economical.
The adapter circuit can also be used, if desired, as a conventional relay device in a vehicle having a single combined stop/turn signal lamp circuit on each side so that the trailer lamps operate in exact correspondence with the vehicle lamps; this usage has the advantage of not requiring heavier duty components, such as flashers and switches, in the existing vehicle system.
The foregoing features along with additional advantages and benefits of the invention will be seen in the ensuing description and claims which are to be considered in conjunction with the accompanying drawing.